| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | October 18, 1988 |
| PATENT TITLE |
Method of purifying L-ascorbic acid |
| PATENT ABSTRACT | A method of purifying L-ascorbic acid which comprises: bringing an acidic aqueous solution of L-ascorbic acid which contains a cationic surfactant into contact with active carbon activated by chemicals. The method is in particular useful for removing a cationic surfactant from a reaction mixture of diacetone-2-keto-L-gulonic acid or 2-keto-L-gulonic acid with a mineral acid in the presence of an inert solvent and a cationic surfactant, to produce L-ascorbic acid |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | July 1, 1986 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT REFERENCES CITED |
Ikuo Abe et al, Chemical Abstracts 85:51333y. M. Takashio et al, Chemical Abstracts 90:56246k. M. Layard et al, Chemical Abstracts 103:110485q; Journal de Chimie Physique (1985), vol. 82(4), pp. 415-419. English Translation of Japan 53/98,955. |
| PATENT CLAIMS |
What is claimed is: 1. A method of purifying L-ascorbic acid which comprises: (a) preparing an acidic aqueous solution of L-ascorbic acid which contains an alkylamine and has a pH of not more than 5 from a reaction mixture of a reaction of diacetone-2-keto-L-gulonic acid or 2-keto-L-gulonic acid with a mineral acid in the presence of the alkylamine and a solvent inert to the resulting L-ascorbic acid, the reaction mixture containing the precipitated L-ascorbic acid, the alkylamine, water, the solvent and acetone as a by-product, by adding water to the reaction mixture sufficient to dissolve the precipitated L-ascorbic acid, adding an alkali in amounts equivalent to the amount of the mineral acid in the mixture to neutralize the mineral acid, separating the resultant aqueous layer from the mixture, and removing the acetone from the solution; and (b) bringing the acidic aqueous solution of L-ascorbic acid which contains an alkylamine into contact with active carbon activated by a member of the group consisting of zinc chloride, phosphoric acid and calcium chloride. 2. The method as claimed in claim 1 wherein the active carbon is active carbon activated by zinc chloride. 3. The method as claimed in claim 1, wherein the aqueous solution contains L-ascorbic acid therein in amounts of 10-30% (W/V). 4. The method as claimed in claim 1, wherein the aqueous solution contains the alkylamine therein in amounts of 50-5000 ppm. 5. THe method as claimed in claim 1, wherein the aqueous solution has a pH of 1.5-2.5 |
| PATENT DESCRIPTION |
This invention relates to a method for purifying L-ascorbic acid, and in particular, to a method of purifying L-ascorbic acid by removing therefrom a cationic surfactant contained in L-ascorbic acid produced from diacetone-2-keto-L-gulonic acid or 2-keto-L-gulonic acid in the presence of a cationic surfactant. A process is already known for producing L-ascorbic acid in which diacetone-2-keto-L-gulonic acid or 2-keto-L-gulonic acid is reacted with a mineral acid in the presence of a solvent inert to the resulting L-ascorbic acid, such as an aromatic hydrocarbon, and a cationic surfactant, and then the resultant L-ascorbic acid which crystallizes out is separated from the reaction mixture usually by filtration, as disclosed in Japanese Patent Publication No. 48-15931. This process provides L-ascorbic acid in high yields, and the cationic surfactant is removed therefrom in the purification step of L-ascorbic acid. Although it is already known that the treatment of an aqueous solution of L-ascorbic acid which contains a small amount of iron effectively removes the iron from the solution, as disclosed in Japanese Patent Disclosure No. 53-98955, but no method has been hiterto known which makes it possible to industrially and advantageously remove the cationic surfactant from the resultant L-ascorbic acid. An object of this invention is therefore to provide a method of purifying L-ascorbic acid, and in particular, to provide a method of removing a cationic surfactant contained in L-ascorbic acid. A method of purifying L-ascorbic acid of the invention comprises: bringing an acidic aqueous solution of L-ascorbic acid which contains a cationic surfactant into contact with active carbon activated by chemicals. The method of the invention is applicable to any aqueous solution of L-ascorbic acid which contains a cationic surfactant, however, the method is in particular useful for removing a cationic surfactant from a reaction mixture obtained by the process for producing L-ascorbic acid, as mentioned hereinbefore. Such a reaction mixture may be obtained by reacting diacetone-2-keto-L-gulonic acid or 2-keto-L-gulonic acid with a mineral acid in the presence of an inert solvent and a cationic surfactant. The method of the invention is industrially and advantageously utilizable for the removal of a cationic surfactant from such a reaction mixture. As an aspect of the invention, the reaction mixture as above is treated as follows before the contact with active carbon. Since the reaction mixture contains L-ascorbic acid precipitate, water is first added to the reaction mixture to dissolve the precipitate, an alkali is added to the mixture in amounts equivalent to the amount of the mineral acid in the mixture to neutralize the mineral acid, and then the aqueous layer is separated from the mixture. The thus obtained aqueous solution contains L-ascorbic acid together with a cationic surfactant and by-products such as acetone, and is acidic, usully at a pH of 1.5 to 2.5. The aqueous solution may then be contacted with active carbon activated by chemicals, which being hereinafter referred to as chemicals-activated carbon. However, it is preferred that the solution is distilled to remove the acetone and then the resultant insoluble substance is removed therefrom by filtration, to provide an aqueous solution which usually contains L-ascorbic acid in amounts of 10-30% (W/V) and a cationic surfactant in amounts of 50-5000 ppm. In the method of the invention, it is preferred to put this solution into contact with chemicals-activated carbon. In the prior art, the resultant precipitate of L-ascorbic acid is separated by filtration and purified by washing. However, since the resultant L-ascorbic acid in the reaction mixture is a muddy substance composed of very fine precipitates, it is difficult to fully remove the solvent therefrom, but also the resultant cake is readily cracked to make the washing of the cake incomplete. Further, the reaction mixture as obained is corrosive to filtration apparatus since the reaction mixture contains a mineral acid as well as an organic solvent, so that it is difficult to choose a filtration apparatus which stands both the mineral acid and organic solvent. The method of the invention is superior to the above prior method of purification of L-ascorbic acid. According to the invention, the precipitate of L-ascorbic acid in the reaction mixture is dissolved by adding water to the reaction mixture, and an alkali to neutralize the mineral acid therein, and then the aqueous layer is separated from the inert solvent. The resultant aqueous solution therefore contains a less amount of impurities than the initial reaction mixture is obtained, and the solution, preferably after further removal of the by-produced acetone, for example, by distillation in vacuo, is put into contact with chemicals-activated carbon, to remove effectively the cationic surfactant. The cationic surfactant contained in the aqueous solution of L-ascorbic acid includes, for example, quaternary ammonium salts such as stearyltrimethylammonium chloride, alkylamines such as stearylamine, distearylamine, dimethylstearylamine, stearylpropylenediamine or stearylpropylenediamine dioleate, alkylpyridinium salts such as an alkylpyridinium chloride. The aqueous solution containing such a cationic surfactant is made contact with chemicals-activated carbon in an acidic condition usually at a pH of not more than about 5 in the invention. According to the invention, it is necessary to use chemicals-activated carbon to remove effectively a cationic surfactant from an aqueous solution containing the cationic surfactant and L-ascorbic acid. The active carbon may be powder or granular. Active carbons activated by gas, for instance, by steam, are ineffective for removing a cationic surfactant from L-ascorbic acid. The chemicals-activated carbon usable in the invention is not specifically limited, but preferably has pores of not more than 15 .mu.m in diameter in pore volume not less than 0.7 cc/g, and pores of not more than 300 Angstroms in diameter in pore volume not less than 0.4 cc/g, wherein the pores of not more than 300 Angstroms in diameter have an average pore diameter of not less than 17 Angstroms. As well known, the pore volume of pores of not more than 15 .mu.m in diameter may be determined by mercury porosimetry, nitrogen adsorption method, etc, as described in "Adsorption," pp. 95-113 (1967), Kyoritsu Shuppan K.K. The pore volume of pores of not more than 300 Angstrom in diameter may be determined also by the nitrogen adsorption method. The average pore diameter (d) of pores of not more than 300 Angstrom in diameter is calculated from the equation: d=4v/s wherein v is the pore volume of pores of not more than 300 Angstrom in diameter on the asumption that they are cylindrical in the form, and s is the specific surface area calculated from the BET adsorption isotherm of nitrogen gas. However, the above pore properties are only illustrative, and are not critical in the invention. The chemicals-activated carbon as specified as above may be produced, as is well known, by immersing wooden material such as wood, sawdust, or coconut shell in chemicals such as zinc chloride, phosphoric acid or calcium chloride, baking the thus treated material at temperatures of about 600.degree.-700.degree. C., and removing the chemical used by washing the baked material with an acid, e.g., hydrochloric acid. Among these active carbons, however, is most preferred an active carbon produced by zinc chloride-activation. The chemicals-activated carbon may be powder or granular, and the latter is preferred. More specifically, granular active carbon is most preferred which contains granules of 8-250 mesh (according to JIS) in amounts of not less than 90%. These chemicals-activated carbon are availble as commercial products, such as "Special Shirasagi" and "Strong Shirasagi" for chromatography by Takeda Chemical Industries, Ltd. Any method is adoptable to bring the aqueous solution of L-ascorbic acid which contains a cationic surfactant into contact with the chemicals-activated carbon. For instance, the solution may be simply mixed with the active carbon, followed by filtration to remove the active carbon, or the solution may be put into contact with the active carbon by the use of fixed bed, moving bed or fluidized bed of the active carbon. The contact of the solution with the fixed bed active carbon is industrially advantageous, in which the solution is passed through a column having the active carbon filled therein upwardly or downwardly, since the fixed bed contact is easy in operation and high in adsorption efficiency of cationic surfactant to the active carbon. The cationic surfactant is adsorbed onto the active carbon and separated from the solution while L-ascorbic acid is contained in the resultant effluent. The amount of the chemicals-activated carbon used is dependent upon the method in which the solution is made contact with the carbon and adsorption utility of the carbon as well. However, when the fixed bed active carbon is adopted, it is preferable to use the active carbon in amounts of 2-10% by weight based on L-ascorbic acid in the solution. The used active carbon may be regenerated by a known method, for example, by washing the carbon with an acid, alkali or an organic solvent. After the removal of the cationic surfactant, the aqueous solution of L-ascorbic acid may be treated in any conventional manner to provide purified L-ascorbic acid. Usually the solution is concentrated to crystallize out L-ascorbic acid. |
| PATENT EXAMPLES | This data is not available for free |
| PATENT PHOTOCOPY | Available on request |
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